Instruments such as endoscopes define an interior volume which is sealed during normal operation in order to, among other things, protect sensitive internal components of the instrument. Maintaining a seal to the interior volume during normal operation of the instrument also simplifies cleaning and sterilizing the instrument after use.
Although the instrument remains sealed in normal operation, there are circumstances in which it is desirable to temporarily break the seal to the interior volume. For example, in the case of air transport it is desirable to break the seal to the interior volume of the instrument in order to prevent a potentially damaging positive pressure differential between the interior volume of the instrument and the relatively lower pressure of the atmosphere inside the aircraft at high altitude. A positive pressure differential applied to an endoscope, for example, may cause elastic expansion in flexible sheathing material associated with the probe of the instrument. This expansion may result in elastic fatigue which eventually damages the material and may ultimately cause the material to rupture.
In the case of cleaning or sterilization, a sealed instrument may be subjected to conditions which produce both positive and negative pressure differentials between the interior volume of the instrument and the atmosphere in which the instrument is located. Positive pressure differentials during cleaning or sterilization pose the same threat noted above in relation to air transport. Negative pressure differentials may also damage certain components of the instrument.
Sealed instruments may also be subjected to testing which produces pressure differentials between the instrument interior volume and the surrounding atmosphere. An endoscope, for example, may be tested for leaks by opening a port in the endoscope body to apply a small positive pressure to the interior volume of the instrument, and then submerging the instrument in a liquid. Any leak in the instrument is apparent as the gas in the interior volume escapes through the leak and forms bubbles in the liquid.
In the field of endoscopes, it is known to take measures to avoid potentially damaging pressure differentials and thereby avoid damage which may be caused by such differentials. U.S. Pat. No. 5,807,238 shows a sterilization cap which is attached to an endoscope prior to subjecting the instrument to a sterilization process. The sterilization cap is adapted to attach to a sealed port on the endoscope, the port being sealed by a valve which remains closed during normal operation of the instrument. The sterilization cap disclosed in U.S. Pat. No. 5,807,238 includes two separate check valves, and is adapted to open the valve of the sealed port as the cap is attached. One check valve is configured to open in response to a predetermined positive pressure differential between the interior volume of the instrument and the surrounding atmosphere, while the other check valve is configured to open in response to a predetermined negative pressure differential between the interior volume of the instrument and the surrounding atmosphere. U.S. Pat. No. 5,807,238 also discloses using a filter or membrane in the sterilization cap in order to prevent sterilizing liquids from reaching the interior volume of the instrument while still allowing gasses to pass into and out of the interior volume of the instrument when the sterilization cap is installed.
A problem with the arrangement shown in U.S. Pat. No. 5,807,238 is that the sterilization cap must be manually attached to a normally closed/sealed port of the endoscope in order to facilitate the desired pressure relief. Should the sterilization cap be connected incorrectly to the instrument or not installed at all prior to air transport or a sterilization procedure, the instrument remains sealed and may be damaged by positive or negative pressure differentials which may arise.